Mechanical convergence fixture apparatus and method

ABSTRACT

A mechanical convergence fixture apparatus (10) having an LCD frame assembly (12) which is positioned in relation to a projector chassis (14) using an alignment assembly (12) which is positioned in relation to a projector chassis (14) using an alignment assembly (16). The LCD frame assembly (12) has a micro LCD (24) rigidly affixed thereto and a field lens (32) adjustably affixed thereto. A vacuum chuck (40) holds the LCD frame assembly (12) on the alignment assembly (16) while the LCD frame assembly (12) is positioned. A drop of adhesive (62) is then placed on each of a plurality of locating studs (18) and a like plurality of locating holes (20) to affix the LCD frame assembly (12) in position on the chassis (14). The alignment assembly (16) is then detached from the LCD frame assembly (12) to be reused.

TECHNICAL FIELD

The present invention relates to the field of mechanical focusing andconvergence devices for optical systems, and more particularly to animproved mechanical convergence fixture for projection-type liquidcrystal projectors. The predominant current usage of the inventivemechanical convergence fixture is in commercial video projection deviceswherein accuracy of adjustment, economy of manufacture and ruggednessare all important factors.

BACKGROUND ART

In a liquid crystal projector, white source light is separated intobeams of its three primary colors. Each beam is then infused with animage by a liquid crystal light valve or micro-LCD. Finally, the threebeams are recombined into a single image and projected onto a displaydevice (a screen).

The micro LCD's generate a representation of the image to be projectedby using many small picture elements or pixels. Therefore, the abovementioned beams of light that emerge from the micro-LCD's are pixellatedrepresentations of the particular color components of the image. Thus,an accurate projected image requires that the pixels of the threeinfused beams be precisely aligned during the recombination step,meaning that the micro-LCD's themselves must be carefully positioned. Inorder to optimally orient the micro-LCD's the following requirementsmust be met.

(1) 6 degree of freedom (dof) adjustment capability must be available.Both rotation and linear translation with respect to three perpendicularaxes are required in order to ensure that proper image alignment can becaused to occur.

(2) Adjustment mechanisms must have high resolution controls. Because ofthe small size of the pixels, direct manual adjustments are too crude toachieve proper alignment. Some sort of interface must be provided whichcan transform relatively large-scale operator inputs into micro-LCDmotions of a magnitude commensurate with the pixel size.

(3) Adjustment mechanisms must provide positive positioning constraints.Since multiple operations are required to tune all 6 degrees of freedom,intermediate adjustments must have some amount of resistance to motion.Positioning devices typically have some sort of final locking mechanism,but to activate and deactivate that mechanism numerous times over thecourse of adjustment is cumbersome and often impossible. Therefore, anyrobust positioning device must provide for physical locating effects,rather than relying on balance, gravity or friction.

(4) The individual magnification of each image must be independentlyadjustable. There must be a means for making slight adjustments to theprojected size of the image from any projection device. This means mustbe simple, inexpensive, and easy to use such that adjustments can bemade quickly during the production process. Conventional positioningsystems have either provided limited adjustment capability or else haveuse complicated mechanisms. For example, in U.S. Pat. No. 5,418,586issued to Fujimori, a light valve positioning system is disclosed whichuses a combination of plates, posts, and screws to provide the full 6degree of freedom adjustment capability. However, while the mechanismtaught by Fujimori provides a significant improvement in the field, itutilizes 6 major components and 14 adjustment screws. In addition, inspite of Fujimori's own listing of problems associated with eccentricpins (manufacturing difficulty, increased part count due to supportingcomponents, non-linear relationship between rotational input and lineartranslation output, and the like), the mechanism of Fujimori stillincludes three such pins. Also, the mechanism of Fujimori utilizes anumber of direct manual adjustments, making precise control difficult.For instance, a typical adjustment procedure used according to theFujimori teachings is represented in the rotation of the liquid crystalvalve about a vertical axis. This procedure involves rotating a flathead screwdriver in a slot formed by a notch in a light fixing plate anda hole in a lower adjustment plate. In this operation, the scales of theoperator inputs are completely out of scale compared to the requiredadjustments, making proper alignment impossible. In addition, becausethe adjustment actuator (the flat head screwdriver) is removed once thedesired rotation is achieved, the position of the light fixing plate isnot positively secured, This allows motion to occur during the actualfixing process when the fixing screws are tightened, potentially causingmisalignment of the liquid crystal light valve.

Many of these concerns have been addressed in a copending patentapplication Ser. No. 08/970,957 entitled MECHANICAL CONVERGENCE DEVICEFOR MICRO-LCD, which has an inventor in common with this presentinvention. The MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD provides allof the requirements discussed above and avoids the pitfalls. Indeed, forsome applications the MECHANICAL CONVERGENCE DEVICE FOR MICRO-LCD may besuperior to the present invention. However, the MECHANICAL CONVERGENCEDEVICE FOR MICRO-LCD is still quite complicated and is relativelyexpensive to manufacture.

It would be advantageous to have a device for positioning a micro LCD ina projection device so as to provide for optimal accuracy of adjustmentand ruggedness, while maintaining optimal simplicity and economy.However, to the inventor's knowledge, no prior art method or means hasachieved this combination of goals. Such devices have all been either tocomplicated and expensive and/or too difficult to adjust, or else havebeen overly delicate and/or expensive to produce.

DISCLOSURE OF INVENTION

Accordingly, it is an object of the present invention to provide anoptical-mechanical convergence device which will provide for accurateand easy positioning of a liquid crystal display ("LCD") in a projectionapparatus.

It is still another object of the present invention to provide a methodand apparatus for positioning a micro-LCD which is economical tomanufacture. It is yet another object of the present invention toprovide a method and apparatus for positioning a micro-LCD which isrugged in that the position of the micro-LCD will not shift whensubjected to normal shock and vibration.

It is still another object of the present invention to provide anapparatus and method for adjusting the magnification of each devicechannel in an LCD projector in order to make all projected images thesame size.

Briefly, the preferred embodiment of the present invention is a framefor securing a micro-LCD to an associated field lens. The frame ispositioned in relation to a chassis using an external three axis linearstage (alignment assembly) and, when in position, is affixed with anadhesive to a plurality of locating studs which are rigidly affixed tothe chassis. The expensive alignment assembly is the removed. Thealignment assembly is then an assembly device rather than a component ofthe shipped product, thereby greatly reducing the cost of the shippedproduct.

An advantage of the present invention is that, since size and expense ofthe adjustment mechanism are not critical (since the adjustmentmechanism stays behind to be reused), then the adjustment mechanism canbe made to be very accurate and easy to use.

A further advantage of the present invention is that the micro-LCD canbe very accurately positioned and held in place.

Yet another advantage of the present invention is that the micro-LCD isrigidly affixed on a very light frame which is not readily susceptibleto shock and vibration.

Still another advantage of the present invention is that the per unitexpense is greatly reduced.

Yet another advantage of the present invention is that an opticalelement (a field lens) can be re-positioned axially to provide slightadjustments of the magnification of the individual image devices,thereby allowing very high resolution alignment.

These and other objects and advantages of the present invention willbecome clear to those skilled in the art in view of the description ofthe described mode of carrying out the invention and the industrialapplicability of the preferred embodiment as described herein and asillustrated in the several figures of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a mechanical convergence fixtureapparatus according to the present invention;

FIG. 2 is an exploded view of the LCD frame of FIG. 1; and

FIG. 3 is a perspective view of the alignment apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The invention is presently embodied in a mechanical convergence fixtureapparatus. The inventive mechanical convergence fixture apparatus isdepicted in a diagrammatic view in FIG. 1 and is designated therein bythe general reference character 10. The mechanical convergence fixtureapparatus 10 has a liquid crystal display ("LCD") frame assembly 12which is intended to be affixed to a chassis 14 using an alignmentassembly 16, as will be described in more detail hereinafter.

The chassis 14 is that portion of the projection mechanism into whichlight is projected through the LCD frame assembly 12. As discussedpreviously herein in relation to the prior art, the chassis 14 for acolor projector will have mounted thereto three of the LCD frameassemblies 12, one for each of the primary light colors. As can be seenin the view of FIG. 1, the chassis 14 has a plurality (four, in thepresent example) of locating studs 18, and the LCD frame assembly has alike plurality of locating holes 20 for sliding over the locating studs18 so as to generally place the LCD frame assembly 122 in position onthe chassis 14. It should be noted that the fit of the locating studs 18within the locating holes is not tight, such that there can be someminor movement of the LCD frame assembly 12 in relation to the chassis14 before the LCD frame assembly is finally affixed in place in themanner to be discussed hereinafter.

FIG. 2 is an exploded perspective view of the LCD frame assembly 12. Aframe 22 has a micro LCD 24 affixed thereto by a pair of pan head screws26 using a pair of washers 28. The micro LCD 24 as used in the presentinvention is not different from that used in conjunction with prior artapparatus. An aperture stop (mask) 30 is provided between the micro LCD24 and the frame 22 for limiting projected light to the generallyrectangular shape intended. A gasket 32 is provided to seal the junctionbetween the is micro LCD 24 and the frame 22 so as to prevent dustand/or other contaminants from entering. The shape of the gasket 32 willbe dependent upon the exact shape of the frame 22, such that a generallycomplete seal is created between the frame 22 and the micro LCD 24.

A field lens 33 is housed within a lens cell 34 which is mounted to theframe 22 in an adjustable manner so as to permit adjustment of thespacing between the field lens 33 and the micro LCD 24 which, in turn,permits adjustment of the magnification. In this embodiment, the lenscell 34 has a threaded collar 36 for mating to a lens attachment ring 38on the frame 22 which is threaded in like manner on the inside.

FIG. 3 is a perspective view of the alignment assembly 16. A vacuumchuck 40 is provided for selectively holding the LCD frame assembly 12in place on the alignment assembly 16. Apparatus for selectivelyproviding vacuum to the vacuum chuck 40 is well known in the art and isnot specifically depicted in the view of FIG. 3.

The alignment assembly 16 has a rotation stage 42, a two axis goniometer44 and an X,Y,Z linear stage 46. The rotation stage 42, the goniometer44 and the linear stage 46 are each commercially available parts whichare well known to those skilled in the art and are available fromseveral different manufacturers. The rotation stage 42, the goniometer44 and the linear stage 46 each move the vacuum chuck 40 (with the LCDframe assembly 12 of FIG. 2 affixed thereto) in relation to a commonorigin 48. The rotation stage 42 rotates the LCD frame assembly 12 abouta Z axis using a rotation adjustment screw 52. The goniometer 44 adjuststhe LCD frame assembly 12 about the X axis 54 and a Y axis according tothe position of two goniometer screws 58. The linear stage 46 adjuststhe position of the LCD frame assembly 12 linearly along the X, Y and Zaxis (50, 54 and 56) using the three linear stage screws 60 depicted inFIG. 3.

Various modifications may be made to the invention without altering itsvalue or scope. For example, the alignment assembly 16 could be a custommade singular apparatus rather than the assemblage of "off the shelf"components as described herein. Another example of a likely modificationwould be to temporarily affix the LCD frame assembly 12 to the alignmentassembly 16 by means other than the vacuum chuck 40 as described herein.

All of the above are only some of the examples of available embodimentsof the present invention. Those skilled in the art will readily observethat numerous other modifications and alterations may be made withoutdeparting form the spirit and scope of the invention. Accordingly, theabove disclosure is not intended as limiting and the appended claims areto be interpreted as encompassing the entire scope of the invention.

INDUSTRIAL APPLICABILITY

As previously discussed herein, it is critical that the micro LCD 24 beprecisely located in relation to the chassis 14, because the focus andconvergence of the images from the three micro LCD's 24 will otherwisenot be correct. It is also critical that the magnification of eachchannel be essentially identical, otherwise absolute convergence of allpixels cannot be achieved. According to the present inventive method,the positioning of the LCD frame assembly 12 is accomplished by affixingthe LCD frame assembly 12 temporarily to the alignment assembly 16 usingthe vacuum chuck 40, and then positioning the LCD frame assembly 12 inrelation to the chassis 14 using the adjustment screws 52, 58 and 60 ofthe alignment assembly 16. The magnification of each image is thenadjusted by repositioning the optical element (field lens 32) relativeto the micro LCD 24 by turning the threaded lens attachment ring 38.

When the LCD frame assembly 12 is correctly positioned (as determined byvisual inspection of the projected image by the operator, or by othercriteria as may be established), the LCD frame assembly 12 ispermanently affixed to the chassis 14 by placing a drop of adhesive 62(FIG. 1) on each of the locating studs 18 and at least partially withineach corresponding locating hole 20. An additional drop of the adhesive62 is placed on the threaded collar 36 to hold the field lens 33 inplace. In the embodiment described herein, the adhesive 62 is an epoxy,although many other types of adhesive or other bonding means might beused for the purpose. Thereafter, the LCD frame assembly 12 is detachedfrom the alignment assembly 16 (by releasing vacuum from the vacuumchuck 40 in the embodiment . It should be noted that, according to thedescribed embodiment of the present inventive method, three iterationsof the inventive apparatus will be employed such that images of allthree colors can be cooperatively adjusted.

According to the present invention, it will be easier to correctlyposition the LCD frame assembly 12 and such positioning will generallybe more accurate, due in large part to the fact that the alignmentassembly 16 can easily be more robust and precise than comparablecomponents which must be made small enough and inexpensive enough toleave attached to the chassis 14 to be shipped with the final product.Yet another aspect of this is the fact that the marginal cost ofalignment apparatus is reduced to essentially nothing, given that thealignment assembly 16 is not shipped with the final product, and may bereused time after time. The ability to separately adjust the field lens33 position provides the ability to compensate for both magnificationand focus errors between colors, thus enabling a converged and wellfocused image to be attained. A key to this is the provision of acompensation mechanism that allows for correlation of tolerance errorsthat typically arise in high resolution imaging systems due tomanufacturing limitations--which limitations are avoided or at leastoptimally reduced as described herein.

According to the present invention, a compensation mechanism whichallows for correction of typical tolerance errors in high resolutionmulti-channel imaging systems is provided. The magnification and focuscan be adjusted independently on each channel to achieve well convergedand focused images. There is an aperture stop 30 that is part of theassembly. The micro LCD 24 can be aligned to the aperture stop 30 with ahigh degree of accuracy. The field lens 33 can be independentlypositioned relative to the display device (the micro LCD 24) and themain housing (the chassis 14). This is accomplished with a minimumnumber of parts and yet a dust sealed airspace next to the displaydevice is provided.

The invention allows convergence to sub-pixel accuracy over the entireimage. The magnification and focus of the image in each channel can beadjusted slightly to accommodate manufacturing tolerances in the lensesand display devices. The assembly is constructed in such a way that theair space between the display device and the field lens (nearest opticalelement) is sealed to prevent the entrance of dust particulate. Thedisplay device can also be accurately aligned to the aperture stop whichis placed directly against the device. This is all done withoutresorting to parts which are expensive to manufacture or assemble. Theinventive method for aligning and converging images has shown itself tobe invaluable for small high resolution display devices, particularly asthe resolution of such devices is increasing. To the inventor'sknowledge, no comparable results have not been attained with any priorart devices.

The unique design of the LCD frame assembly 12 provides an elegantlysimple solution to the problem of positioning and holding the micro LCD24 in relation to the chassis 14, as used in accordance with the presentinventive method. Since the mechanical convergence fixture apparatus 10of the present invention may be readily produced and incorporated intothe design and production of micro LCD projection systems, and since theadvantages as described herein are provided, it is expected that theutility and industrial applicability of the invention will be bothsignificant in scope and long-lasting in duration.

I claim:
 1. A method for affixing an LCD to a projection chassis havinga first LCD positioned thereon, comprising:a. temporarily affixing theLCD to an alignment assembly; b. aligning the LCD in relation to theprojection chassis to converge images generated by the LCD and the firstLCD; c. permanently affixing the LCD to the projection chassis; and d.detaching the LCD from said alignment assembly; whereinthe LCD is amicro LCD rigidly affixed to an LCD frame assembly; the LCD frameassembly includes a field lens; the LCD frame assembly includes anadjustment mechanism for adjusting the position of the field lens inrelation to the micro LCD; and the position of the field lens isadjusted in conjunction with step b.
 2. An LCD frame for holding a microLCD in relation to a projection chassis, comprising:a rigid frame havinga generally rectangular mask to which the micro LCD is rigidly affixed;a field lens adjustably affixed to the LCD frame such that the fieldlens can be moved in relation to the micro LCD; and a plurality oflocating holes for locating the LCD frame over a like plurality oflocating studs on the projection chassis.
 3. The LCD frame of claim 2,and further including:an adhesive for affixing the locating holes inrelation to the locating studs.
 4. The LCD frame of claim 2, and furtherincluding:an adjustment mechanism which is temporarily affixed to theLCD frame for positioning the LCD frame in relation to the projectionchassis.
 5. The LCD frame of claim 2, and further including:an aperturestop rigidly affixed in relation to the LCD frame.
 6. The LCD frame ofclaim 2, and further including:an adhesive for fixing the position ofsaid field lens in relation to the micro LCD.
 7. The LCD frame of claim2, and further including:an aperture stop rigidly affixed to the LCDframe.
 8. The LCD frame of claim 2, and further including:a gasket forpreventing the intrusion of particulate matter within the LCD frame. 9.A mechanical convergence fixture apparatus for positioning a micro LCDin relation to a projector chassis, comprising:a frame for holding themicro LCD; and an alignment assembly for temporarily holding andpositioning the frame in relation to the projector chassis; whereinsaidalignment assembly is removed from said frame after said frame ispositioned in relation to the projector chassis; and a field lens ismovably affixed to said frame such that the position of the field lensrelative to the micro LCD is adjustable.
 10. The mechanical convergencefixture apparatus of claim 9, wherein:the field lens is affixed to theframe by a threaded ring such that turning a housing of the field lensmoves the field lens in relation to the micro LCD.